Organic chemistry, naming cycloalkenes

[TheRedDevil18]

Homework Statement

Homework Equations

The Attempt at a Solution

Shouldnt the name for that be 3-fluoro-2-methyl cyclopentene instead of 4-fluoro-3-methyl cyclopentene ?, if not can someone explain to me why ?

 

[DrClaude]

From the IUPAC rules:

In cycloalkenes the double bond carbons are assigned ring locations #1 and #2. Which of the two is #1 may be determined by the nearest substituent rule.

 

[TheRedDevil18]

The carbon at the top, on the tip of the pentagon, because if you number clockwise from that carbon the methyl will be on the second carbon and the fluoroide on the third.

 

[DrClaude]

The carbon at the top, on the tip of the pentagon, because if you number clockwise from that carbon the methyl will be on the second carbon and the fluoroide on the third.

Did you read the rule? Let me quote again: the double bond carbons are assigned ring locations #1 and #2. If you number the top carbon #1, then you have to go counter-clockwise for the other double-bond carbon to be #2.

 

[TheRedDevil18]

Did you read the rule? Let me quote again: the double bond carbons are assigned ring locations #1 and #2. If you number the top carbon #1, then you have to go counter-clockwise for the other double-bond carbon to be #2.

Oh, I see it now, so it should definately be 4-fluoro-3-methyl cyclopentene. Thanks for making it more clearer

 

[DrClaude]

Just to add a further point of detail: if you take the top C to be #1 and go counter-clockwise, you get 4-fluoro-5-methyl cyclopentene. The nearest substituent rule then tells you to set the top C to #2 and count clockwise to get 4-fluoro-3-methyl cyclopentene.